Mercury 50hp 4 stroke alarm

[JWeislocher]

I have a 2002 Merc 50hp 4 stroke that has been alarming at wot. I am under the assumption that it is an overheat alarm. I have replaced the impeller and changed the oil a week ago.

The problem is when running anything over about 1/3 throttle I get an alarm. The alarm doesn't occur immediately but goes off after I have gone about 100-200 yards. If I back off the throttle the alarm goes away. I have not had the alarm occur while idling, but I usually dont leave the motor idling for any long period of time. If I rev the motor with the fast idle lever and leave it idle at higher a rpm I do not get the alarm.

Under the assumption that this is an overheating problem I removed the thermostat and did a boil test. The thermostat did not open and I do plan to change it. But in my thinking, shouldn't the motor overheat at idle as well if the thermostat is not opening?

 

[woody66912]

Re: Mercury 50hp 4 stroke alarm

Not necessarily , but i do think you are on the right track. A thermostat change out is a good way to find out if your impeller is bad. It's much easier and quicker then changing a pump.

 

[BillP]

Re: Mercury 50hp 4 stroke alarm

I had an early mariner/merc 50x4s (powerhead made by yamaha) and it ran for 10 yrs without issues. But a pal of mine who is a certified merc mech told me the early 50hp had a corrosion problem where the water tube plugged into the powerhead. They used a steel or something grommet that rusted and restricted water flow. He said is was a big problem but merc didn't recognize it publicly. He repaired a bunch of the rental 50s on pontoon boat fleets that were affected after only one year. Might be worth a look but it's major $$$ taking the powerhead off to check...nothing like a 2 stroke.

bp

 

[JWeislocher]

Re: Mercury 50hp 4 stroke alarm

I had an early mariner/merc 50x4s (powerhead made by yamaha) and it ran for 10 yrs without issues. But a pal of mine who is a certified merc mech told me the early 50hp had a corrosion problem where the water tube plugged into the powerhead. They used a steel or something grommet that rusted and restricted water flow. He said is was a big problem but merc didn't recognize it publicly. He repaired a bunch of the rental 50s on pontoon boat fleets that were affected after only one year. Might be worth a look but it's major $$$ taking the powerhead off to check...nothing like a 2 stroke.

bp

I have heard about the infamous grommet corrosion problem. I'm going to run through all of my other options first. If worst comes to worst I will pull the powerhead myself and check the grommet.

 

[BillP]

Re: Mercury 50hp 4 stroke alarm

Pull the sending unit and clean it. Could be dirty enough to hold heat. Clean it even if it looks ok because even one that looks ok can be dirty enough to give bogus signals.

Also, my 50 x 4 was really sensitive to impellers. It would heat up after idling a long time when the impeller was starting to go bad. It ran normal temp at high rpm. Just for laughs I did a side by side comparison of impellers of my omc 3hp and the 50. The 3 was way larger and lasted yrs under heavy use. The 50 x 4 lasted 50 hrs max and I changed it about 10 times. There is no extra beef for wear and any gasket leaks in the cooling system could pose a problem. Some things to think about when beating your head against the wall.

 

[72 Fury]

Did you ever solve the overheating?

 

[GA_Boater]

Did you ever solve the overheating?

Stop posting in old threads.

Closed.